Beijing Daxing International Airport is ranked as one of the Top Seven Wonders of the New World by the Guardian. The airport uses drum-shaped welded hollow spherical joints in the steel roof structure. This study measured the tensile and compressive strengths of a full-scale model of the drum-shaped welded hollow spherical joints and analyzed the joint failure mechanism. A finite element model was then used to study the effects of the drum position, stiffening rib arrangement, drum size, wall thickness, and sphere diameter on the ultimate bearing capacity of the joints after verification of the model against test data. Design methods and calculational formulas were developed based on the full-scale test data and the finite element analyses to predict the axial tension and axial compression loadbearing capacities of drum-shaped welded hollow spherical joints.
The terminals' operating characteristics of energy use and indoor environment must be well understood, which is of great significance to guide the construction of green airport that minimize the energy usage while providing good indoor service quality. These must be well understood to guide the construction of airport terminals that minimize the energy usage while providing quality indoor environments. This study was based on questionnaires of the energy consumption of 22 terminals in China and measurements of the indoor environmental quality in 9 terminals in different climate zones in China. The results show that the annual electricity consumption of Chinese airport terminals is 129~281 kWh/(m2·a) or 0.79~3.15 kWh/person with averages of 180 kWh/(m2·a) and 1.90 kWh/person. The air conditioning and lighting systems are the largest power draws, accounting for 61% and 17% of the total building electricity consumption. During the summer, the temperature and humidity in public areas meets the level I comfort level standard with less than 50%. During the winter, the temperature and humidity normally meet the level Ⅱ comfort level with 71%~96%. Conditions can become out of compliance on very hot summer days due to high solar radiation levels or on warm winter days due is overheating. The surveys also show that the average indoor CO2 levels are less than 700×10-6 in the terminals. The natural lighting in most public areas in the building during the day reaches 300~500 lx, with the nighttime illumination being far less than the standard requirement of 200 lx. The indoor noise levels are high with averages between 55 and 70 dB and some minimums higher than 60 dB even without announcements. The results were further combined with subjective questionnaires of 4 500 passengers to identify 10 key issues and to recommend 11 technical and management methods to reduce energy use and improve indoor air quality and building services. This research agrees well with current design practices and research on energy saving and indoor air quality improvement in airport terminals, which also provides a solid data foundation, scientific technical support and guarantee for the construction and development of green airports in China.
Spraying trajectory optimization is important for ensuring high quality coatings because the trajectory directly affects the coating formation. This paper describes a trajectory optimization method for planar spraying. Efficient, high quality planar spraying is realized by solving a complementary spraying gun model. As for NURBS free-form surfaces, artists use different size brushes to create finer features on some objects than on others. This concept of variable size brushes is implemented here by changing the distance from the spray gun to the surface for free-form surfaces. The spraying is further optimized on complex surfaces by varying the spraying speed. Simulations and tests show that the film thickness uniformity is 1.64% worse and the paint utilization rate is 13.54% higher when spraying flat surfaces but that the film thickness uniformity is improved from 31.68% to 4.79% when spraying free-form surfaces. The results verify the effectiveness of this method for free-form surfaces.
Motion sickness is a common problem when traveling. Research has shown that nearly 1/3 of the population suffers from motion sickness when travelling by sea, land and air. The pathogenesis of motion sickness is complex with no unified conclusions. The sensory conflict hypothesis holds that motion sickness is mainly caused by mismatches of vestibule, vision and proprioception. Since a driver does not need to operate a car when using automatic driving, the feeling conflict is intensified and the automatic driving is less comfortable. This study investigates physiological indexes which can be used to quantitatively evaluate motion sickness. The experiments used a 6-DOF simulator platform combined with a virtual reality (VR) system to simultaneously provide visual and vestibular stimulation to the subjects. The subjective motion scores and EEG (electroencephalogram) signals of 11 healthy subjects were recorded during automatic driving and active driving scenarios to compare the motion responses of the subjects during the two driving scenarios. Analyses of the motion scores and the EEG records show that the subjects' motion scores were 2 points higher during automatic driving than during active driving with increases of motion sickness related to increases in the gravity frequency based on the power spectral density of the θ waves in the motor center (FC2, Cz), sensory center (CP5, P3) and visual center (POz) of the brain during automatic driving. The paired t test showed correlation between the gravity frequency differences based on the power spectral density of the subject during active driving and automatic driving (p < 0.05). The results indicate that subjects are more likely to develop motion sickness during automatic driving and that EEG signals can be used to quantitatively evaluate the degree of motion sickness.
This study investigated whether transcranial direct current stimulation can increase the visual attention span and the controlling mechanism for this effect through EEG (electroencephalogram) analyses. Seven healthy subjects participated in three experiments on three different days for comparison. Two stimulation protocols, anodal and cathodal stimulation, were performed on the dorsolateral prefrontal cortex with sham stimulations used in control tests. The visual attention span of the anodal stimulation group was significantly improved compared with the control (p=0.034 7), while that of the cathodal stimulation group was significantly reduced (p=0.029 4). The EEG records showed that the prestimulus alpha power was significantly reduced in the anodal stimulation group with difficulty string lengths of 3~5. The result indicated that transcranial direct current stimulation can modulate the prestimulus Alpha power which influences the visual attention span.
An optimized inverse kinematic algorithm was developed for 7 degrees of freedom (7-DoF) manipulators with an S-R-S kinematic structure that avoids joint limits. The first step determines the closed-form solution of the inverse kinematics model based on the arm angle parameter. The result is then used to determine feasible arm angle intervals for the given joint limits. Then, an optimal weighted target function is defined to avoid the joint limits with the weights determined according to the joint positions. The relations between the joint angles and the arm angles are then linearized to simplify the complex optimal target function to a quadratic function. The optimization problem that includes the feasible arm angle intervals then avoids the joint limit. This intuitive, efficient algorithm is effective, avoids the joint limits and can be computed online.
The slider is an important component of a servo press and its mass directly affects the punching accuracy and manufacturing cost. Some servo presses have bad slider structures and the sliders are too heavy. This paper presents a lightweight slider design method based on its layered structure using different optimizations. A load analysis model is developed to determine the boundary conditions for an ANSYS optimization analysis. Then, the connection and support of the upper part of the slider are analyzed using topology optimization to remove the maximum amount of material. The design parameters for the lower part of the slider are then optimized to optimize the separator thickness and layout. Finally, ANSYS is used to verify the overall optimized design. Thus, the slider mass is reduced while still ensuring sufficient rigidity of the slider. The method given in this paper provides an effective design method for lightweight mechanical products.
A high stiffness, high load loading mechanism was developed for machine tool reliability tests. A kinematics model was used to analyze a singularity in the motion and develop a dynamic model with the Jacobian matrix used to evaluate the speed transfer efficiency of the loading mechanism. The kinetic energy was modeled to define the inertia matrix and evaluate the acceleration. The results show that the three-axis loading mechanism has good acceleration in the Z direction and good isotropy in the XY plane. The acceleration provides sufficiently fast motion in the Z direction.
Smoke diffusion caused by the stack effect and the blocking effect in a sloped tunnel was investigated in a full-scale fire experiment under a stationary vehicle on an urban rail transit line. The ventilation mode and the vehicle blocking were varied to study the effects of the airflow velocity, the vertical distribution of the smoke temperature, the smoke layer distribution and the smoke spread time. The results show that the ventilation mode and the vehicle blocking both change the flow field near the fire which in turn influences the airflow velocity, smoke distribution and smoke spread time. A smoke spread velocity model was then used to further study the smoke diffusion for various vehicle blocking conditions. The conclusions can guide smoke control design and personnel evacuation plans for such tunnel fire scenarios.
The opposed-flow flame spreading along a polymethyl methacrylate (PMMA) sheet was investigated numerically. The melting process included a mushy transition region in the energy equation during the flame spreading. The fuel was ignited by applying a fixed heat flow at one position on the upper boundary of the material. The results show the typical procedures of ignition followed by unstable to stable flame spreading. The morphology of the mushy zone and the molten phase thickness were obtained based on the temperature field. The results show that the mushy zone is thin near the flame front and gradually thickens downstream of the flame front. Additionally, the melt region is shallow near the flame front and gradually deepens with increasing the distance from the flame front. The numerical results and a scale analysis show that the melt interface location can be approximated by a quadratic function.